[S-SS07] Environmental Seismology: from deep earth to surface process

[SSS07-P17] Experimental Study on the Impact of Different Coupling Conditions on Distributed Acoustic Sensing (DAS) Passive Surface Wave Dispersion Analysis

*YUN HUANQIN¹, Pingsong Zhang¹, Chaoqiang Xi¹, Shiang Xu², Binyang Sun¹, Shenglin Li² (1.School of Earth and Environment, Anhui University of Science and Technology, 2.State Key Laboratory of Digital and Intelligent Technology for Unmanned Coal Mining, Anhui University of Science and Technology)

Keywords:Distributed Acoustic Sensing, DAS, Passive surface wave, Dispersion

In the fields of subsurface exploration and geotechnical engineering, passive surface wave dispersion analysis based on ambient noise is an important technique for studying the structural characteristics of subsurface media, particularly in determining the shear wave velocity (S-wave velocity) of shallow soils and rocks. Traditional seismic exploration methods, such as conventional seismic sensors, typically require large-scale equipment and high costs, while Distributed Acoustic Sensing (DAS) technology offers an efficient and cost-effective alternative. However, the commonly existing communication fiber optic networks in urban areas often experience fiber suspension in wellbores, which may result in poor coupling conditions.
This study designed four different coupling configurations, including: communication optical fibers installed in wellbores, sensor-enhanced optical fibers installed in wellbores, communication optical fibers fixed to the ground surface, and sensor optical fibers fixed to the ground surface. The goal was to investigate the impact of various coupling conditions on DAS passive surface wave dispersion analysis. The choice of coupling condition significantly affects the quality of DAS signals and the accuracy of surface wave dispersion curve extraction, particularly in complex urban environments where coupling methods can notably influence the propagation characteristics of the signals.
By comparing the effects of different coupling methods on DAS signal quality, the following key conclusions were drawn: First, DAS surface wave dispersion quality lies between that of vertical geophones and horizontal component geophones, indicating that DAS signals have good adaptability in surface wave dispersion analysis. Second, under different coupling conditions, fiber optic sensors fixed to the ground surface outperform those installed in pipelines, and signals of sensor optical fibers are of higher quality compared to those of communication optical fibers, highlighting the significant impact of pavement types on surface wave signal propagation. Furthermore, sensor optical fibers provide more stable signal quality compared to communication optical fibers. Finally, by applying cross-correlation processing to DAS data, higher-order surface wave energy can be effectively recovered, offering strong support for high-resolution subsurface media detection.